Glass mirrors have long been used as vision-aiding devices in vehicles. It is well known that the typical glass used in such mirrors is very weak in tension, havng a relatively low tensile strength approximating 3,000 psi. Such low tensile strength has caused problems in producing adequately safe mirrors consistent with modern safety standards in the United States and other countries. For example, the normal inside rearview mirror in an automobile is positioned adjacent the upper portion of the windshield and may easily be struck by the head of a person within the automobile during an accident. Since the human head is generally spherical in shape, the impact of a head against the front of a mirror produces a spherical contact area placing the rear surface of the mirror in tension in both longitudinal and transversal or widthwise directions. Given the low tensile strength of the glass, the glass tends to fracture quite easily upon such impact. Various attempts have been made to overcome this problem such as by fully supporting the back of the mirror with plastics and other materials and the like.
Another problem in the design of safety mirrors is that of retaining and preventing the scattering of glass fragments from a mirror should the mirror be struck with an impact large enough to break it. Thus, gross fracture of the mirror must be prevented to avoid protruding, jagged mirror edges which could cause gross lacerations of a person's head upon impact. Various attempts have also been made to increase the shatter resistance of mirrors and to retain broken fragments.
Further, it is well known that automobiles and other vehicles including rearview mirrors are used in climates in various parts of the world having greatly differing temperature extremes. Typically, a mirror must be able to withstand and function without distortion of the visible image in the broad temperature range of -40.degree. F. and up to approximately 250.degree. F. (encountered in closed vehicles in hot climates). Accordingly, the problem of designing an adequate safety mirror which is distortion free, breakage and shatter resistant as well as fragment-scattering resistant has been hampered by the additional criterion that such mirrors must meet these criteria in extremes of temperatures.